A dual mast S/R vehicle is used in automatic storage systems to transport large and heavy goods along an aisle to a designated storage compartment within a rack or structure usually when the maximum weight of such goods exceeds the lift and/or carrying capacity of a single mast S/R vehicle. Dual mast S/R vehicles are known and commercially used in the art.
Generally, dual mast S/R vehicles comprise three operational degrees of freedom. The first degree of freedom constitutes a direction of movement, generally described as down-aisle, whereby each vehicle accesses the position of each addressable column of material stored along an aisle of a S/R facility. Material is stored on shelving or the like in horizontally and vertically addressable arrays such that inventory is transported between the arrays and the S/R vehicle in a direction normal to the aisle, generally referred to as cross-aisle. The second degree of freedom comprises operation of a shuttle which is mounted on a vertically driven carriage and moves cross-aisle to the material storing arrays whereby inventory is retrieved and stored. The third degree of freedom comprises vertical drive for the carriage. This invention provides novel apparatus and methods for down-aisle and vertical movement of large and heavy loads of goods.
Presently available dual mast S/R vehicles comprise two masts disposed upon a single base and supported by a drive wheel on one end and and idler wheel on the other end of the base. Vertical drive for the carriage comprises a cable drum, a motor, and a power transfer assembly. The cable drum is rotated by the motor and power transfer assembly to wind and unwind attached lift cables, thereby lifting and lowering the carriage. For tall masts, the cable drum for a dual mast S/R vehicle is mounted cross-aisle and due to cross-aisle width limitations the cable system is limited to 2 pulls. The preferred embodiment is a right angle speed reducer connected directly to the motor and the motor is disposed at right angles to the cable drum. Large motors, required by dual mast S/R vehicles, are therefor usually mounted upright.
Each of the two masts are substantially symmetrically disposed on the single support beam near the ends of the beam to thereby be separated by the length of the carriage. In this position, any bending of the base due to forces of the combined mast, carriage and load weight, tips the bottom of the two masts toward each other while the top spacing is maintained by the beam mast cap. Thus, the long span between the wheels and the total load supported in a single beam results in the need for special mast to base shimming or the base member to have much higher cross sectional properties to reduce mast deflections, caused by bending of the base, to acceptable levels for safe carriage operation when transporting maximum loads. Such required increases in cross section nearly doubles the height of a dual mast supporting base over a single mast supporting base. The increased loading of the base and masts on only two wheels requires that the wheel diameters as well as the wheel bearing size be increased. Each of these increases place an additional burden upon equipment used in the manufacture of dual mast systems. Further, increases in beam cross section and supporting wheel and bearing sizes increase the height of the lowest elevation (low bay) a carriage may serve, adding complications in building design and reducing the effective volume of storage space.
In current art, a single rigid interconnecting mast cap beam is employed to connect the two mast tops together. The cap comprises a moment transmitting, rigid joint in each end. The mast cap is only fractionally as strong as the mast and carries the same which can moments exerted by the bending masts. Thus, as masts deflect in response to a bending base and forces comprising vehicle running loads are added thereto, moments caused by the mast top movement against the restraining cap beam results in stresses great enough to possibly break the joint bolts and to crack rigid steel joint members at the tops of the masts.
Presently available dual S/R vehicles comprise vertical drive components of vertical drive assemblies which are individually mounted on the dual mast S/R vehicle structure. As such, the presently available vertical drive assemblies are assembled and tested only after the major dual mast S/R vertical drive assembly supporting components, which usually comprises an assembled vehicle, are available at the job site.
All dual mast S/R vehicles must conform to the clearance requirements of the aisle where used. Such requirements predefine a significant width limitation on allowable dimensions of dual mast S/R vehicles and parts assembled thereon. In the past, such limitations have led to the development of dual mast S/R vehicles which employ vertically mounting of large motors, and, therefore, right angle speed reducers to translate vertical motor rotary motion in horizontal plan to a horizontal drum vertical rotary motion which winds and unwinds a vertically disposed lift cable.
Generally, dual mast S/R vehicles comprise a mounting frame, a motor mounted to the frame, and a drum assembly which raises and lowers the carriage by winding and unwinding at least one carriage supporting lift cable. A speed reducer is commonly used between the motor and drum to translate relatively high rotational speed of the motor to a lower rotating speed required of the cable winding and unwinding drum.
In the present art, there are two methods of mounting a motor relative to the position of the drum. The first method comprises mounting the drum directly to the speed reducer output shaft and, thereby, directly coupling the motor to the drum along a common axis. In-line connections among the motor, speed reducer, and drum, severely limit the collective and individual sizes of motors, reducers, and drums and cable pull configurations which may be used and yet stay within the above mentioned width limitation, especially in dual mast systems.
To solve problems provided by the first method, the second method, comprises a vertically disposed and mounted motor and a right angle motor to drive the horizontally disposed drum. A power translation device, capable of withstanding low speed, high torque, driving forces, is disposed between the motor and drum. The drum, for a high mast dual mast S/R vehicle, can only wrap the cable length from a two pull cable system and keep the dual mast S/R vehicle within cross-aisle dimensional limits.
The second method has improved space, orientation, and speed flexibility over the first method, but requires a chain be used as the power translation device to drive the drum at the site of maximum tension. Commonly, such use of chains requires frequent maintenance and constant lubrication. Further, chains most often use tensioners which push against the side of the chain to maintain proper tautness in the chain. There is no tensioning required in the first method.
Generally, the present art uses a brake mounted on the end of the motor. Such brakes are usually electrically released, spring acutated axial disc brakes. Such braking is ineffective in the event of chain failure.